In conventional optics, a lens can be used to refract a spherical wave, which is radiated from a point light source located at a focus of the lens, into a plane wave. Currently, the converging effect of the lens is achieved by virtue of the refractive property of the spherical form of the lens. As shown in FIG. 1, a spherical wave emitted by a radiator 30 is converged by a spherical lens 40 and exits in the form of a plane wave. The inventor has found in the process of making this invention that, the lens antenna has at least the following technical problems: the spherical lens 40 is bulky and heavy, which is unfavorable for miniaturization; performances of the spherical lens 40 rely heavily on the shape thereof, and directional propagation from the antenna can be achieved only when the spherical lens 40 has a precise shape; and serious interferences and losses are caused to the electromagnetic waves, which reduces the electromagnetic energy. Moreover, for most lenses, abrupt transitions of the refractive indices follow a simple line that is perpendicular to a lens surface. Consequently, electromagnetic waves propagating through the lenses suffer from considerable refraction, diffraction and reflection, which have a serious effect on the performances of the lenses.